The invention refers to a residual differential device for a multipolar current breaking appliance which has a power supply derived from the system voltage by a diode bridge rectifier circuit connected to more than two polyphase supply wires.
The electronics of residual differential devices requires a certain energy to function and one distinguishes between the so-called "own current" or detected-current supplied differential devices in which the energy is borrowed from the fault current itself, and the auxiliary source devices in which the energy is supplied by an independent source or by the controlled electrial system. The own current differential devices ensure complete security, the supply being automatically available in the event of a fault. Two types of auxiliary source devices are known. With the first type the security of the device is ensured by an automatic tripping system in the event of a lack of voltage from the source. These known devices, not being able to start again on their own in the event of the auxiliary source reappearing, have the disadvantage of not ensuring a continuity of operation, which is often unacceptable particularly for appliances assembled as switchboards. With the second type, the security is only obtained if the electrical continuity of all the auxiliary source wires is ensured. Effectively, if a single phase circuit is considered, in the event of a break in the neutral wire, the supply from the auxiliary source and at the same time the operating security are no longer ensured while the risk of a fault in the phase wire continues. To alleviate this disadvantage, it has previously been proposed to double or multiply the supply sources and, particularly in the device of the type mentioned above in which the energy is supplied by the controlled electrical system, to provide several supply wires, particularly phasse and neutral ones and if necessary earth. The risks of failure are thereby considerably reduced, but a dangerous situation may result if one or several of the sources are faulty and the appliance functions with a single supply source which could itself fail.
The present invention has as its aim the remedying of this disadvantage and the possibility of production of a totally safe residual differential device.